1. Field of the Invention
The subsurface pump of the present invention relates generally to the field of downhole pumps used in wells to pump liquids such as water and oil, and more particularly to rod-driven pumps for recovering oil from subsurface formations.
2. Description of the Prior Art
Subsurface pumps are used in water wells and in oil wells in a variety of environments to pump fluids of widely varying flow characteristics.
Conventional rod-driven subsurface pumps include a cylindrical housing disposed in the well casing in the subterranean area of oil production. Typically a rod string, the sucker rod, extends into the pump housing and is connected to a plunger contained within the housing. The sucker rod is reciprocated thereby causing the plunger to move upwardly and downwardly. A stationary or standing valve is typically located at the bottom of the pump controlling flow of liquid into the pump housing. Liquid flows into the pump housing on the up stroke. The stationary valve limits flow into the housing during the down stroke.
An upper, traveling valve reciprocates with the sucker rod. The traveling valve opens during the down stroke due to the pressure of fluid trapped between the plunger and the stationary valve. Opening of the traveling valve allows fluid to flow into the pump housing above the valve, which fluid is forced upward on the up stroke of the rod and plunger. Significant pressures are generated due to the compression of fluid between the plunger and the stationary valve.
Conventional subsurface pumps typically include a ball and seat arrangement for the standing valve and for the traveling valve. The seat is typically provided below the ball, with the ball contained within a cage, the cage limiting upward movement of the ball.
In conventional arrangements, the plunger is on the up stroke before the traveling valve is engaged. A quantity of fluid escapes through the seat prior to engagement of the ball. The downward flow of fluid forces the ball to the bottom of the cage and onto the seat. This closing mechanism creates high velocity fluid flow at the interface of the ball and seat, the fluid often containing particulate matter, such as sand. Erosion of the ball and seat and reduced pumping capacity result.
Conventional pumping units, utilizing a traveling valve and a standing valve, are subject to high impact pressures on the valves due to fluid between the traveling valve and the seating valve or due to columnar fluid and the reciprocation of the plunger. The impact pressures, gas pounding or liquid pounding, result in wear and failure of the pump.
The following United States patents are indicative of the prior art.
Adams, et al., U. S. Pat. No. 1,549,175 discloses a rod-driven, double acting hollow plunger pump including a standing tube and a double-walled plunger, the standing tube contained between the walls of the standing tube.
Adams U. S. Pat. No. 2,160,811 discloses a rod-driven, traveling barrel pump including two spaced pairs of sealing surfaces on the barrel and plunger defining an annular space that is vented to the interior of the plunger.
Grise U.S. Pat. No. 2,413,044 discloses means for priming a grease pump including a pump cylinder, a priming cylinder and associated ball and seat valves.
Wells U. S. Pat. No. 3,212,444 discloses a multizone rod-driven pump for use in slim-hole wells including upper and lower plungers, the upper plunger and rod having a passageway in communication with the lower section of the upper pump barrel.
Simon U.S. Pat. No. 4,219,311 discloses a rod-driven pump having a fluid communication passage bypassing a valve to limit gas or liquid pounding.
Fekete U. S. Pat. No. 4,740,141 discloses a pump having a piston plunger with a valve, a valve ring, and a valve plug disposed in the plunger.
Simon, deceased et al. U.S. Pat. No. 4,596,515 discloses a rod-driven pump having a valve operable near the end of the downward rod stroke for the passage of fluid into the pump chamber to limit gas or liquid pounding.